Monohalogenation of hydrocarbons



Dec. 8, 1959 v c. E. ADAMS EI'AL 2,916,527

MONOHALOGENATION 0F HYDROCARBONS Filed Nov. 22, 1957 2 Sheets-Sheet 1 LIQUID HYDROCARBON- FEED GASEOUS I HALOGEN- FEED FRACTIONATION HALOGENATION TOWER FIGURE l LIQUID HALOGENATED PRODUCT rClOfk Adms Inventors Charles N. Kimberlin, Jr

Aflomev Dec. 8, 1959 c. E. ADAMS EIAL 2,915,527

MONOHALOGENATION OF HYDROCARBONS Filed NOV. 22, 1957 2 Sheets-Sheet 2 REFLUX CONDENSER HYDROCARBON FEED NITROGEN CHLORINE COLUMN BELLOWS PUMP FIGURE 2 [Clark E. Adams Chqfles N Kimberlin, J: lllVGlltOfS paratus for the halogenation of hydrocarbons.

' mono-halogenated hydrocarbons.

hydrocarbons.

.tivity of mono-halogenated hydrocarbons.

as is, normal in fractional distillation art. "fractionationshalogenation tower,. fractionation-chlo- Unite Clark Edward Adams and Charles Newton Kimberliu,

. J12, Baton Rouge, La., assiguors to R550 Research and Engineering Company, a corporation of Delaware Application November 22, 1957, Serial No. 698116 Claims. (Cl. 260-660) The present invention relates to a process and ap- More particularly, it relates to the process and apparatus for preparing monohalides from petroleum hydrocarbon streams. Still more particularly, the invention relates to the process and apparatus for halogenating liquid hydrocarbons with a high selectivity to monohalides by countercurrently contacting the halogenwith a high molecular excess of hydrocarbons in a fractionation tower designed for high liquid holdup in the upper portion of the tower.

-It is known that olefinic hydrocarbons are desirable components of refined motor fuels. One method of making such olefinic fuels is to halogenate petroleum naphtha and then convert the halogenated hydrocarbons to olefinic hydrocarbons by dehydrohalogenation. In order to avoidthe formation during dehydrohalogenation of diolefins, which subsequently form undesirable polymers and gums, the halogenation step must be operated so that a high selectivity to monohalides-as opposed to -dihalides and polyhalideswill be formed.

Prior methods to achieve a high selectivity of monohalides have not proven altogether satisfactory. High molar ratios of hydrocarbon to halogen have been fed to the halogenation zone to prevent polyhalide formation, but of course this requires very highliquid throughput and thus added apparatus expense in order to process a given amount of material.

Incremental addition of gaseous chlorine in portions of the total amount required has been attempted, but this process necessitates an undesirable plurality of towers or recycle steps.

It is an object of the present invention to produce it isa further object to provide an economic process. for producing monohalogenated hydrocarbons in afractiorlation column to the substantial exclusion of diand poly-halogenated A further object is to provide a fractionation halogenation tower economically designed with ahigh liquid holdup zone in the upper portion of the tower in order to allow for maximum yield and selec- These and further objects will become apparent as the invention is more fully described hereinafter.

.There are two attached diagrams. Figure l is a schematic drawing of a commercial fractionation-halogenation tower of this invention. Figure 2 is a schematic drawing of. the experimental apparatus employed for purposes of illustration.

It has now been discovered that high selectivity to mono halogenated hydrocarbons. may be obtained by conducting halogenation in a "fractionation-halogenation tower designed for high liquid holdup in the upper portion, or reaction zone, of the tower, and low liquid holdup in the lower portion, or fractionation zone, such The terms rination tower, 'and the like, will be' used herein to denote a fractionation column wherein both the designated 2,916,527 Patented Dec. 8, 1959 ice reaction and fractionation of the reaction product take place. These towers are normally of the tray type, such as bubble-cap tray towers, sieve plate towers, etc., which permit liquid holdup above the trays.

Hydrocarbons are generally halogenatedin the liquid phase, with one hydrogen atom of thehydrocarbon'molecule being replaced by one halogen atom of the diatomic halogen molecule to form the monohalide. Chloride and bromine are the most frequently used halogens in this general type of reaction because of their availability and suitable reactivity, and since they are gases under the reaction'conditions.

Suitable hydrocarbons are those having 4 to 50 carbon atoms, preferably 6 to 20, or those boiling in a range between 35 and 900 F., preferably between 150 and 650 F. The boiling range of the hydrocarbon feed must be below the boiling range of the halogenated product, in order to allow rapid separation. Selected cuts'from petroleum fractions such as naphtha, gas oil, kerosene, cycle stocks, etc., may be halogenated according to the present invention. The naphtha hydrocarbons boiling in a range between 150 and 400 F. are the preferred feeds for this invention because the olefins ultimately produced therefrom are particularly useful as high octane components in gasoline blends.

In the operation 'of this invention the halogen is bubbled up through the fractionation-halogenation tower in countercurrent contact with the liquid hydrocarbons. The tower is operated such that gaseous hydrogen halide is removed overhead and the liquid monohalogenated hydrocarbons as bottoms. More specifically, liquid hydrocarbons and gaseous halogen are countercurrently contacted in the upper portion of the fractionation halogenation tower, hydrogen halide vapors are removed overhead, and liquid halogenated hydrocarbons and unreacted hydrocarbons descend to thelower portion of the tower. In the lower portion, fractionation. causes the unreacted hydrocarbons to boil up; thus the hydrocarbon vapors ascend to the upper portion of the tower to further and will rapidly be removed from the upper portion to. the

lower portion of the tower, thereby avoiding further 'halogenationin the upper portion to form the diand poly-halides.

The novel feature of the tower lies in its design in the upper portion, or reaction zone, for high liquid holdup, thereby allowing reaction of the halogen in the presence of a large excess of hydrocarbons in this upper, reaction zone. This feature may be accomplished by a number of tray tower designs. Preferred in the present invention are the bubble-cap tray towers, a specific embodiment of which is shown inthe attached Figure 1.

7 Referring now to Figure 1, the fractionatiomhalogenation tower is represented by the character 1, and consists of a reaction zone A which includes all trays above the halogen inlet'line and a fractionation zone B which includes. all trays below the halogen inlet line. The preferred towers may have between 10 and trays, preferably between 15 and 30 trays, with 1 to 20 of these trays, preferably 2 to 10, in the upper portion, or reaction zone, and 9 to.80, preferably 13 to 20, in the lower portion, or fractionation zone. For purposes of illustration only, 6 trays arevshown inthe diagram, 3 in each zone.

The liquid levels in the upper portion or reaction zone A, are much further elevated, e.g. .2 to IOItimesfurther elevated, from the trays 2 than are the liquidlevcl's'in the lower portion, or fractionation zone B, elevated from trays 3. The positions of weirs 4 and downflow pipes 5 as compared to weirs 6 and downflow pipes 7 are the significant factors in this novel tower construction. The lower end of each of the downflow pipes 5 and 7 is sealed in the liquid on the tray to which it delivers. The weirs, over which the liquid flows into the downflow pipes, may be of various shapes-circular, straight, slightly curved, etc. .The bubble caps 8 and 9 remain unchanged over the prior art, and may be of any conventional design, e.g., round bell caps and tunnel, or rectangular, caps, etc. adapted to allow efiicient contacting of gas and liquid.

The operation of the diagrammed apparatus will be better understood after the following description of the flow of hydrocarbon and halogen through the column. Liquid hydrocarbon feed is fed through line 10 into the top of column 1. As the liquid descends it is held for suflicient periods in the reaction zone, by means of the construction hereinbefore described, to provide a large excess of the hydrocarbon over the gaseous halogen, which is fed via line 11 in about an equimolecular proportion to the hydrocarbon feed. The halogen flows upwards through bubble caps 8, countercurrently contacting and dispersing in the descending excess hydrocarbon in the reaction zone. Gaseous hydrogen halide passes upwards through vapor-risers and bubble caps 8 and is removed via vent line 12. A reflux condenser 14 is provided in the top of the tower in order to condense any hydrocarbon leaving the upper plate. The liquid mixture of hydrocarbons and halogenated hydrocarbons descends over weirs 4 and through downflow pipes 5 and eventually into the lower portion, or fractionation zone, of the column, which is in communication with the upper reaction zone like any two of the various trays, viz, by means of a downflow pipe. In this fractionation zone, liquid holdup is low, relative to the holdup in the upper reaction zone, but normal, relative to common fractionation practice. Heat is supplied via heating coil 13, thereby causing the unreacted hydrocarbons to vaporize, pass through vapor-risers and bubble caps 9, and return to the reaction zone to comprise part of the desired excess of hydrocarbon. The remaining liquid halogenated hydrocarbons pass over weirs 6, downwards through downflow pipes 7, and are discharged via line 15 as a product containing about 85 to 98% of the monohalides, 15 to 2% of the diand poly-halides, and negligible amounts of unconverted hydrocarbon. This stream may be passed to a separate distillation tower, scrubbers, etc., to yield essentially pure monohalides. The tower may also be operated so that pure monochlorides are removed as a side stream via line 19 with polychlorides removed from the bottom of the tower. The reaction zone of the column is provided with cooling coils 16 in order to remove the excess heat liberated by the exothermic halogenation reaction. Lights 18 may be provided in the reaction zone, since light, particularly ultraviolet light, enhances or catalyzes the reaction of halogens with hydrocarbons.

The feeds of hydrocarbon and halogen are introduced in a molecular ratio of between about 0.9 and 1.1, preferably in about an equirnolecular ratio. Despite this ratio, the hydrocarbon is in great excess in the upper portion of the column, because of the novel construction of the tower. An excess of hydrocarbon equivalent to a mole ratio of hydrocarbon to halogen of at least 10/1 preferably at least 20/ 1, and up to 200/1, or higher, is required for this invention. Thus, high selectivity to the monohalogenated hydrocarbons may be achieved without requiring the high throughput of hydrocarbons heretofore required.

It has been stated earlier that the halogenation reaction is highly exothermic, often requiring means for cooling the reaction mixture. The reaction temperature is not critical in this invention and its control is well within the scope of those skilled in the art. The same is true 4 of the pressure, for each of these conditions is dependent upon the other as well as upon the characteristics of the hydrocarbons being halogenated, e.g. boiling point, reactivity, etc. It is desirable, of course, to maintain at the top of the reaction zone, a temperature essentially below the boiling point range of the hydrocarbons being halogenated in order to minimize loss of hydrocarbon vapors; and it is also desirable to maintain at the top of the fractionation zone a reflux temperature which falls within or above the boiling point range of the hydrocarbons in order to vaporize substantially all the remaining hydrocarbons, but essentially below the boiling point range of the halogenated product to prevent any substantial vaporization of the latter.

Unless otherwise designated, all percentages and ratios are given throughout this application on a weight basis.

The invention was demonstrated in experimental equipment in such a manner as to show accurately the advantages of this invention. However, it is to be understood that the examples are included for purposes of illustration, not limitation, of the invention.

The experimental equipment used in the examples below is shown schematically in the attached Figure 2. It is seen that the apparatus included a fractionation column 101 and a looped tube reaction vessel 102, corresponding to the lower portion B and the upper portion A of the tower shown in Figure l. Fractionation column 101 was a standard 2-inch I.D. Oldershaw column having 20 perforated plates spaced about 1 inch apart and wiers about inch high. Reaction vessel 102 was made from about 30" of 1 LD. glass tubing. It is noted that an upper extension and a side extension of the reaction vessel were made for purposes of connection with the fractionation column 101 and the condenser column 105. Inserted into the reaction column for purposes of introducing chlorine was a /4" ID. glass down tube 103 provided with a fritted glass tip 104 at its lower end. A 1'' ID. glass reflux condenser column 105 provided with tubing 106 for cooling water circulation, was employed above the reaction column. A 2-inch vertical section of the upper extension of the reaction column was packed with stainless steel packing 107 to prevent loss of sprayed liquid from the reaction zone. Additional apparatus included a glass Dry Ice trap 108 to prevent the escape of any liquid with the hydrogen chloride gas, an enclosure 109 equipped with a 3600 A. ultraviolet lamp 110 surrounding reaction vessel 102, a glass still pot 111 and a heating mantel 112 at the base of fractionation column 101, a product drawolf tap 113 consisting of glass tubing with stopcock extending from still pot 111, temperature calibration wells 114 and 115 at the top of column 101 and at still pot 111 respectively, a stopcock 116 to permit liquid withdrawal from reaction vessel 102, a bellows pump 117 for introducing hydrocarbon feed, a glass storage vessel 118 for the hydrocarbon feed, nitrogen and chlorine pressurized tanks 119 and 120, and the necessary connecting glass and rubber tubing and the like.

Operation consisted of initially charging still pot 111 and reaction vessel 102 with about 500 cc. (320 g., 3.7 m.) each of fresh hexane or C naphtha, establishing maximum boil-up in fractionation column 101 which was equivalent to about 7000 cc. of liquid n-hexane or C naphtha per hour, and introducing chlorine with nitrogen to reaction vessel 102 via line 121, tube 103, and glass tip 104. Additional hydrocarbon was introduced when necessary via line 122. Hydrogen chloride gas was released via line 123, and the chlorinated product was withdrawn from tap 113.

Example 1 The equipment of Figure 2 was charged with n-hexane as described above. Maximum reflux was established with a reflux temperature at the top of the fractionation column of F. Chlorine was added at a rate of of one hour.

, condenser but 55.8 g. of product was obtainedafter washing .with water to remove HCl. product gave'the following results:

(5.3 m.) of n-hexane were added to the reaction zone by meansof the feed pump. -Distillation of the product gave the following fractions:

207 g.154 to 230 F.n-hexane feed 6.4 9 g.230 to 262 -F.--2-chlorohexane i8.6. g. -262 to 284 F.--1chlorohexane Although .equi- The molar selectivity of eta/min. into 78 cc. (51.5 g.) of n-hexane over the period Some hexane waslost through the' reflux Distillation of this 19.8 g.--248 to 261 F. 2-chloroh'exane 2.8 g.270 to 275 F.1-chlorohexane 13.1 g.275 -F.+polychlorohexanes These data show only 69% selectivity to monohalides, despite the facts that the chlorine was reacted with a Ex mp e Ihe equipment described previously was used for continuous operation in the chlorination of an Aramco C naphtha (76.0 API Gravity, Engler Distillation: -%@152 F., 95%@15.8 F.). Maximum reflux was initiated with a reflux temperature of 150 F. and a pot temperature of 175 F., and these temperatures were thereafter maintained at about 150 to 160 F. and 175 to 200 F. respectively throughout the run. Chlorine was added at a rate of about 950 cc./min., which provided a mole ratio of naphtha to chlorine equivalent to about 21/ 1. The reaction was carried out for about 36 hours while naphtha feed was added to the reactor to make up for the product withdrawn from the bottom of the still. Under the conditions of operation the product withdrawn contained a small amount of naphtha feed (2%) but this could be reduced to negligible amounts under more carefully controlled conditions. The chlorinated product amounted to 8590 g. of which 6558 g. was monochlorinated product boiling 225 to 284 F. This represents a selectivity of monochlorination of about 81.5%. A portion of the polychloride fraction obtained under these conditions was analyzed by mass spectrometer and showed 6570% dichlorides, 25 to 30% trichlorides and only about 5% tetrachlorides by weight.

Example 3 In order to demonstrate the effect of even higher ratios of naphtha to chlorine than used in Example 2, the conditions used in Example 2 were duplicated as to feed, temperature, etc. except that chlorine was added at a rate of only 120 cc./min. and nitrogen diluent was added with the chlorine at a rate of 260 cc./min. These conditions are equivalent to a mole ratio of naphtha to chlorine of about 170. The product obtained after about 7 hours of operation amounted to 218 g. of which 5 g. was feed boiling 68 to 107 F., 181 g. was monochlo rinated product boiling 107 to 140 C. and 30 g. was polychlorinated product boiling 140 C.+. This distri- --6 -bution represents aselectivity to monochlorinated' prod uct of 88.7%."

Having thus set forth the general nature and embodiments of the present invention, the true scope is now particularly pointed out in the appended claims.

What is claimed is:

1. A fractionation-reactor tower which comprises a substantially vertical cylindrical tower shell containing an upper and lower section, a series of plate members mounted horizontally in both sections and in vertically spaced relation one with the other, means for passing vapor upwardly through said plate members and means for passing liquid contained above said plate members to a lower level, the inlet to said latter means being positioned to maintain higher liquid levels above the plate members in said upper section and to maintain lower liquid levels above the plate members in said lower section, means for introducing feed liquid and gases, means for withdrawing reaction gases and bottoms liquid and means for controlling the temperature of said tower.

2[ A fractionation-reaction tower which comprises a vertical cylindrical tower shell containing upper and lower sections, a series of plate members mounted horizontally within said sections and in vertically spaced relations one with another, downflow pipes mounted in connection with said plate members and inlet means to said downflow pipes, said inlet means to said downflow pipes .being maintained at a higher level above the plate members in said upper section of said tower and at 'a' lower level above the plate members in the lower 'section'of said tower, said inlet means to the downflow pipes and said downflow pipes being adapted to allow downward flow of liquids from the liquid contained above each plate member to a lower liquidlevel being maintained above the next lower plate, means in said plates which permit the upward flow of vapor through the plate members, means for introducing said liquids near the top of the tower and gases near the bottom of said upper section of said tower, means for withdrawing gases near the top of said tower and bottoms liquid near the bottom of said tower, heating means adapted to heat said lower section of the tower and cooling means allowed to cool said upper section of the tower.

3. A fractionation-halogenation tower which comprises a vertical cylindrical tower shell; a series of 10 to plate members mounted horizontally within said shell and in vertically spaced relation one with another, the upper 1- to 20 of said plate members comprising a reaction zone and the remaining, lower plate members comprising a fractionation zone; vertical downflow pipes mounted in connection with said plate members and circular weirs mounted in connection with said downflow pipes, said weirs and downflow pipes extending higher over the plates in said reaction zone than in said fractionation zone and being adapted to maintain liquid levels above the plate members in said reaction zone 2 to 10 times higher than the liquid levels above the plate members in said fractionation zone and to'allow downward flow of liquids from the liquid concentration above each plate member to the next lower liquid concentration; a plurality of vapor risers and bubble caps spaced on the upper side of each of said plate members adapted to allow the upward flow'of vapor through each plate into a liquid concentration thereabove; a liquid feed pipe and a gas vent pipe positioned near the top of said reaction zone; a gas feed pipe positioned between the bottom plate member of said reaction zone and the top plate member of said fractionation zone; a bottoms liquid product withdrawal pipe positioned at the bottom of said fractionation zone; heating means adapted to heat said fractionation zone; and cooling means adapted to cool said reaction zone.

4. A fractionation-halogenation tower according to claim 3 wherein a vapor withdrawal pipe is positioned at the side of said fractionation zone, adapted for the '7 withdrawal of products boiling slightly lower than the bottoms liquid product.

5. A fractionation-halogenation tower according to claim 3 wherein there are between 15 and 30 plate members, 2 to .10 of said plate members being in said reaction zone and 13 to 20 in said fractionation zone.

6. A process for producing monohalides of hydrocarbons which comprises passing a liquid hydrocarbon downwardly through a reaction zone, contacting in said reaction zone said hydrocarbon with a gaseous halogen in a countercurrent manner, maintaining in said reaction zone a high liquid holdup, recovering hydrogen halide gas overhead, passing the resulting liquid hydrocarbon halide reaction mixture from said reaction zone into a fractionation zone, maintaining the liquid holdup in said fractionation zone below that of the liquid holdup in said reaction zone, fractionating the liquid hydrocarbon halide product to substantially free said product of unreacted hydrocarbon, passing said vaporous unreacted hydrocarbon into said reaction zone, condensing said unreacted hydrocarbon in said reaction Zone and recontacting it with additional gaseous halogen feed, withdrawing;hydrocarbon halide product from a lower portion of said fractionation zone.

7. A process according to claim 6 wherein the hydrocarbon is petroleum naphtha boiling in a range between 150 and 400 F. r

8. A process according to claim 6 wherein the halogen is selected from the group consisting of chlorine and bromine.

9. A process according to claim 8 wherein aside stream of hydrocarbon halide vapors is withdrawn from said lower section of the tower, the fractionation temperature being adapted to allow removal of substantially all monohalides in said side stream and removal of substantially all polyhalides in said bottoms stream.

10. A process for producing hydrocarbon monochlorides which comprises: introducing a petroleum naphtha stream, boiling in a range between 150 and 400 F. substantially below the boiling range of the corresponding hydrocarbon monohalides, near the top of a 10 to 1 plate member, two-section bubble'cup tray fraction- .8 ation-halogenation column, the upper section, of: said column having 1 to 20 plate members and the lower section having 9 to plate members, maintaining liquid levels above the plate members, in said upper section 2 to 10 times higher than above the plate members in said lower section; countercurrently contacting the naphtha stream in said upper section with a gaseous chlorine stream introduced near the bottom plate of said upper section, said chlorine ascending through a plurality of vapor risers surmounted by bubble caps ateach tray into the liquid concentration thereabove; continuously cooling said upper section to a temperature sulficiently low to prevent vaporization of substantially all the hydrocarbons; withdrawing the resulting gaseous hydrogen chloride from near the top of the tower; condensing and recycling any hydrocarbon vapors leaving the top plate of said upper section; passing the liquid reaction dispersion downwards into said lower section of the tower; fractionating said dispersion in the lower section at a temperature adapted to vaporize substantially all the hydrocarbons and to prevent vaporization of substantially all. the hydrocarbon halides; passing the resulting unreacted hydrocarbon vapors upwards into said upper section of the tower, said vapors ascending with the chlorinethrough said vapor risers, condensing, and descending with said liquid reaction dispersion; withdrawing the bottom liquid hydrocarbon halide stream from the bottom of said tower; and recovering the monohalides therefrom.

References Cited in the file of this patent UNITED STATES PATEN'rsi 

6. A PROCESS FOR PRODUCING MONOHALIDES OF HYDROCARBONS WHICH COMPRISES PASSING A LIQUID HYDROCARBON DOWNWARDLY THROUGH A REACTION ZONE, CONTACTING IN SAID REACTION ZONE SAID HYDROCARBON WITH A GASEOUS HALOGEN IN A COUNTERCURRENT MANNER, MAINTAINING IN SAID REACTION ZONE A HIGH LIQUID HOLDUP, RECOVERING HYDROGEN HALIDE GAS OVERHEAD, PASSING THE RESULTING LIQUID HYDROCARBON HALIDE REACTION MIXTURE FROM SAID REACTION ZONE INTO A FRACTIONATION ZONE, MAINTAINING THE LIQUID HOLDUP IN SAID FRACTIONATION ZONE BELOW THAT OF THE LIQUID HOLDUP IN SAID REACTION ZONE, FRACTIONATING THE LIQUID HYDROCARBON HALIDE PRODUCT TO SUBSTANTIALLY FREE SAID PRODUCT OF UNREACTED HYDROCARBON, PASSING SAID VAPOROUS UNREACTED HYDROCARBON INTO SAID REACTION ZONE, CONDENSING SAID UNREACTED HYDROCARBON IN SAID REACTION ZONE AND RECONTACTING IT WITH ADDITIONAL GASEOUS HALOGEN FEED, WITHDRAWING HYDROCARBON HALIDE PRODUCT FROM A LOWER PORTION OF SAID FRACTIONATION ZONE. 